The proposed studies will investigate which hormones or factors affect gonadotropin or prolactin secretion by a direct pituitary action. As the animal model, we propose to use stalk sectioned female rhesus monkeys, in which the pituitary gland is isolated from direct hypothalamic influences. Gonadotropin secretion will be restored by long-term pulsatile infusions of gonadotropin-releasing hormone (GnRH). The effects of variations in the frequency and amplitude of the GnRH pulse on FSH/LH ratios will be examined. Direct pituitary feedbacks of estradiol and progesterone will then be investigated. The effects of biogenic amines (dopamine, epinephrine, norepinephrine and serotonin), gaba, substance P and Beta-endorphin on gonadotropin and prolactin release will be compared in intact and stalk sectioned monkeys. Anatomical studies will include examination of the changes in the hypothalamic parvicellular elements following stalk section by immunocytochemistry, with emphasis on the GnRH and substance P systems.